Production of Seminal Fluid

Question 1

What are the main functions of the efferent ductules.

Answer 1

Transportation of sperm to epididymis

Question 2

Identify the main parts of the epididymis.

Answer 2

Head, tail, body

Question 3

Describe the process of transfer of sperm to the epididymis.

Answer 3

• Sperm in the seminiferous tubules in a large V of fluid (washes sperm into rete testis, vasa efferentia, and epididymis)
• 6-12 days to travel through vasa efferentia (efferent ductules) and epididymis

Question 4

Describe what happens to sperm once in the epididymis.

Answer 4

Various products secreted into the seminal fluid in the epididymis

“When sperm first enters the epididymis from the testis, it is very immature and diluted by a relatively large volume of liquid. The smooth muscle of the epididymis pushes the sperm along tubule with slow waves of peristalsis, so that the sperm traverse its entire 20-foot length in about two weeks. During this time the sperm is supplied with nutrients secreted from the lining of the epididymis and incubated while it matures. All defective and dead sperm, along with most of the liquid medium, are slowly absorbed by the body to concentrate the sperm, which can be stored in the epididymis for up to a month. After a month in the epididymis, sperm begin to expire and are absorbed by stereocilia and replaced by younger sperm. As sperm is needed for ejaculation, it moves from the epididymis to the ductus deferens and onward into the male reproductive tract.”

Question 5

What happens if vasa efferentia is blocked ?

Answer 5

If vasa efferentia blocked, seminiferous tubules and testes are blocked

Question 6

Identify the main changes to spermatozoa in the epididymis.

Answer 6

♦ Concentration: Increases 100-fold, from 5 x 10^7/mL to 5 x 10^9.

♦ Sperm modelling: Nuclear condensation and acrosome shaping completed + cytoplasmic droplet shed

♦ Metabolism: Increased dependence on external fructose for glycolytic energy + little oxidative metabolism + increased intracellular pH (due to Na+/H+ exchange) (reach 7.2 to 7.8 in pH, which it needs because of acidic environment in female reproductive tract)

♦ Motility: Increased disulphide bridges between proteins i outer dense fibers of tail + [cAMP] rises in the tail + Acquires the capacity for forward movement

♦ Membrane: Composition of various components change (specific shape required to enter ovum better)

Question 7

Describe the location of the vas deferens relative to the epididymis.

Answer 7

Vas deferens, is at the back of the cord and is the continuation of the epididymis, at the end of the tail.

Question 8

What are the main functions of the vas deferens ?

Answer 8

1) Propels sperm during ejaculation
2) Can also be dilated to store sperm
3) Nourishes sperm with glycoproteins
4) Absorptive features with lysosomes, that get rid of the dead sperm

Question 9

What in the sperm gives it its distinctive yellow/brown color ?

Answer 9

The lipofuscine granules formed by dead cells give the sperm its distinct color.

Question 10

Where is seminal fluid formed ?

Answer 10

Mainly formed in accessory glands.

Question 11

What is the function of seminal fluid ? What is the main problem of seminal fluid ?

Answer 11

Provides nutrients to protect spermatozoa

BUT exploited by infectious agents (e.g. Hep B, HIV).

Question 12

State what components each gland brings to the seminal fluid, and the V contributed by each gland.

Answer 12

• Testes: 0.1-0.2 mL (Spermatorozoa)
• Seminal vesicle (nourishes it): 1-3 mL (Alkaline, gelatinous)
• Prostate (protects it): 0.5-1 mL (Acidic, watery)
• Bulbourethral glands: 0.1-0.2 mL (viscous, clear)

Question 13

What is the V of a typical ejaculation ?

Answer 13

2.5 - 5.0 mL

Question 14

Identify the main constituents of the ejactulate, along with the concentration of each, main source, and function.

Answer 14

♠ Spermatozoa: 50-150/nL, from testes
♠ Fructose: 8-37 mM, from seminal vesicles and ampulla, used for anerobic energy metabolism
♠ Inositol: 1-3 mM, from testes and epididymis, used for osmotic ballast
♠ Citric acid: 5-73 mM, from prostate, used as a Ca++ chelator (depresses semen coagulation)
♠ Glycerylphosphoryl-choline: 2-3 mM, from epididymis, used a source of choline in phospholipid metabolism
♠ Acid phosphatase: from prostate, cleaves choline from glycerophosphoryl-choline

Question 15

What is the function of the penis ? What are the conditions for the penis to fulfill this role ?

Answer 15

The means by which semen is introduced into the female genital tract.

To do this, penis must be turgid, so must undergo haemodynamic changes.

Question 16

Briefly describe the hemodynamic changes which occur for the penis to be able to enter the female genital tract (and then hemodynamic changes following erection).

Answer 16

Regulated through PSNS activation:
♪ Dilatation of arterioles to corpora cavernosa and corpus spongiosum, so engorged by blood

♪ Sinuses along the length of the penis expand

♪ Closing of arteriovenous shunts that normally bypass the corpora cavernosa

♪ Probably also occlusion of veins draining the penis (minimises veinous return)

When SNS takes over (no more sexual arousal), large veins allow venous return and corpora cavernosa and corpus spongiosum are no longer engorged, penis becomes flaccid.

Question 17

Describe the anatomy of the penis, and relate this to erection.

Answer 17

• Dorsal vein, is at the most superficial layer right under the skin, under the dartos fascia.
• Deep dorsal vein between dorsal artery and the dorsal nerve. Any damage to these structures can compromise blood supply of the penis.
• The profunda artery or cavernosal artery (most important artery to erection) of the penis is ramification of internal pudendal

• Corpora cavernosa (two of them) is surrounded by tunica albugina, then Buck’s fascia. These allow elasticity but also limit expansion of c cavernosa to a certain limit (restrict further inflow of blood after that).
“Tunica albugina helps to trap blood in corposa cavernosa, sustaining the erection”.

• Corpus spongiosum also gets engorged with blood
• Veins lie under elastic tissue so stop veinous return.

Question 18

How does arousal occur ?

Answer 18

Arousal can be the result of:

• erotic psychological stimuli (e.g. visual, olfactory)
• tactile stimuli at the level of the brain
• tactile stimuli can also mediate local spinal reflexes

Question 19

Describe the role of the nervous system in reproductive function (both SNS and PSNS).

Answer 19

SYMPATHETIC

• Lower thoracic and lumbar spinal segments
• Maintains flaccidity

PARASYMPATHETIC

• Control center in sacral spinal segments
• Increased activity produces turgidity
• Sexual stimulation results in reactivation of nitrergic nerves and endothelium (latter thanks to parasympathetic action involving ACh acting on vascular endothelial cells). These two release NO which activates gyanylyl cyclase, which catalyses conversion of GTP into cyclic GMC, which active PKG. This in turn causes vasodilation (i.e. relaxation of vascular smooth muscle), which then allows for penile erection.

Each of these is linked with a sensory pathway, with which they synapse at their distinctive spinal segments.
Sympathetic pathway is almost always in control unless penis is aroused. Following ejaculation, parasympathetic/hemodynamic processes are reversed and sympathetic control takes over.

Question 20

Which parts of the penis are most sensitive to tactile stimuli ?

Answer 20

Glans penis

Question 21

Define tumescence.

Answer 21

Usually refers to the normal engorgement with blood (vascular congestion) of the erectile tissues.

Question 22

Describe the NS response following ejaculation. How can this be interfered with ?

Answer 22

Following ejaculation, PDE V enzyme catalyses conversion of cGMP into inactive product (rather than activation of PKG which would result in vasodilation).

Viagra is a PDE V inhibitor.

Question 23

Identify causes for the failure to obtain an erection.

Answer 23

• Mechanical damage to c. cavernosa
• Obstruction of the arteries to the penis
• Drugs that block parasympathetic actions
• Psychological factors (stress associated with high SNS activity, results in NA causing vasoconstriction of penile arterioles and so inhibits erection)

Question 24

Define impotence. What are the main causes of impotence ?

Answer 24

“Inability to achieve or maintain an erection long enough to engage in sexual intercourse”

Smoking and alcohol

Question 25

Describe the nervous control of ejaculation, mentioning the main phases of ejaculation.

Answer 25

Sympathetic mediated:

• ejaculatory center in lower thoracic and lumbar spinal cord
• signs to ducts of genital tract and to bulbocavernosus muscle at the base of the penis

1) Emission Phase
- smooth muscle contraction in walls of the genital tract
- expels semen into urethral bulb

2) Expulsion Phase
- rhythmic contractions of penis and bulbocavernosus muscle
- ejects semen in spurts

Ejaculation is then followed by a refractory phase of 10 minutes to an hour

Question 26

Describe the main composition of the ejaculate.

Answer 26

Composition of the ejaculate is not uniform:

• First component: Prostate (rich in acid phosphatase and citric acid)
• Second component: Vas deferens (rich in spermatozoa)
• Third component: Seminal vesicle (rich in fructose + semenogelin 1)

Question 27

Describe the role of semenogelin 1 in ejaculation.

Answer 27

Semenogelin causes semen to coagulation, then liquefy (form protection layer (accumulation of all secretions together) in the vagina to allow sperm to move better while being protected from acidic environment))